The present invention relates to ophthalmic lenses and prisms and more particularly to an ophthalmoscopic prism utilized in the diagnosis and treatment of the eye.
Gonioscopes or ophthalmoscopic prisms are used for viewing the angle of the trabeculum, the drainage angle, and related structures of the eye. A gonioscope traditionally used is disclosed in U.S. Pat. No. 4,033,679 to Dr. Walter Sussman. This gonioscope comprises a cylindrical optical body having at its proximal end four planar, inclined facets that narrow toward the proximal end. The planar facets are inclined from 20 degrees to 40 degrees relative to the optical axis of the body. The distal end of the lens has a viewing surface that is substantially perpendicular to the optical axis of the cylinder. The proximal end of the lens has a concave surface with its optical center on the optical axis of the lens. The planar facets have a mirrored coating thereon.
The concave surface is designed to be placed in contact with the cornea of a patient. When the ophthalmologist looks through the viewing surface, the internal surface of the facets totally reflects so that the ophthalmologist can for example see the trabeculum. If it were not for this reflective coating, moisture in contact with the planar surfaces would also be seen by the ophthalmologist thus impairing, for example, his view of the trabeculum. In addition, prisms of this type contain additional coatings to protect the reflective coating and many times are required to be housed in holders to prevent damage to the coatings or mirrored surfaces. Finally, prior gonioscopes are made from optical materials such as methylmethacrylate, or have protective surface coatings, and thus are not autoclavable.
The present invention provides an ophthalmoscopic prism that cannot only be autoclaved but also does not require the reflective and protective coatings required of the prior art prisms. The present invention includes an optically transparent body having an optical axis. The distal end of the transparent body has a viewing surface oriented transversely to the optical axis. The proximal end of the body has a concave surface having a curvature complimentary to the curvature of the cornea of a patient. The proximal end of the body has at least one planar surface extending outwardly and distally from a location adjacent the periphery of the concave surface. In addition, the body has an index of refraction that provides total internal reflection when a viewer looks through the viewing surface, even when the planar surface is at least partially wetted with a fluid.